Cyclone Joyce is expected to fully cross the coast of Western Australia today as a significantly weaker system than predicted.

While the worst danger may be over for the Kimberley, Perth could feel the impact of the weather system next week with up to 50 millimetres of rain forecast to fall if the system tracks towards the city.

The category one storm has moved inland of Eighty Mile Beach, west of Wallal Downs and is expected to weaken over the inland Pilbara bringing heavy rain over the weekend.

Bureau of Meteorology forecaster Craig Earl-Spurr said it was unlikely to reach the previously expected strength of category three.

"It's passed Bidyadanga, but sitting near the coast it means that it hasn't strengthened overnight," he said.

"It's expected to continue moving towards the south-west as a category one, and continue to bring gales to the West Kimberley coast.

"Cyclones need time over water to strengthen, and with the previous forecast of it spending that time over water there was a greater risk of it being a stronger system.

"So the good thing about it getting to the coast a bit sooner is that it has less time to develop and we don't expect to see any impacts greater than a category one".

Drenching could reach Perth

Bureau of Meteorology forecaster Callum Stuart said the next concern was possible flooding.

"I guess the bigger risk is when it moves inland through the eastern Pilbara and into the Gascoyne as well with those river catchments through there, so [we're] certainly looking at a similar rain impact," he said.

And Perth could be in for a drenching early next week — or maybe not.

"Perth will be more like early next week so we might cop a bit of rain later on Sunday and into Monday," Mr Stuart said.

"I don't think they're too concerned about flooding with that, but could be some pretty good falls if the system does track over us.

"However, as we've seen in the last 24 hours, there's still a bit of uncertainty so it could just as easily miss us."

The Bureau has predicted Perth could get up to 35mm on Sunday and up to 70 on Monday.